The inventions described below relate to improvements of the type disclosed in U.S. patent application Ser. No. 054,507 filed July 13, 1970 and to be issued on Apr. 11, 1972 as U.S. Pat. No. 3,655,058, said application being incorporated herein in its entirety by reference hereto.
In particular, the present invention provides means for permitting the apparatus of the aforementioned application to better filter a fluid medium such as a gas most commonly air which has been polluted with liquid or solid particulates of very small particulate size (i.e., from 2.0 microns down to approximately 0.2 micron size).
Removal of very small sized foreign matter from air or gas is traditionally accomplished by electrostatic devices or by bag filters. Consideration of the bag filter and its deficiencies will clarify the intent of the present inventions. In order that it be effective with small particles the filter medium must be dense, with fibre size small enough and fibre distribution fine enough to stop the pollutant in question. It has, therefore, inevitably a rather high pressure drop. In addition, as the particulate is filtered out from the air or gas, it collects on the surface of the filter medium, blocks the pores in the medium, and obstructs the flow of air or gas. The pressure drop, therefore, continues to increase as the particulate is filtered out. In most bag filters the medium is either periodically discarded for a clean piece, or intermittently cleaned by one process or another.
In the aforementioned patent application there is disclosed in an improved filtration apparatus, a rotating filter cage in which the centrifugal force field generated by its own rotation keeps the filter medium clean, and unlike a bag filter it does not become loaded with pollutant.
In the aforementioned patent application air enters the inlet of the apparatus, is given a pressure rise and a high centrifugal component, is then forced through the filter cage carrying a filter medium, then subsequently enters a turbine or expander and is guided out of the apparatus by a diffuser through an exit port.
In the preferred construction a conical rotating shell is provided which rotates with the filter cage so that there is little or no gas leakage from it.
Although the above apparatus is perfectly adequate for its intended purposes, the improvements disclosed herein have been made thereto to permit even more efficient filtering to be accomplished particularly where sub-micron particles are to be filtered.
It should also be understood that the improvements disclosed herein will also find use in other situations which would be apparent to those skilled in the art.